1. Field of the Invention
The present invention relates to a process for preparing a polymeric piezo-electric material composed of a vinylidene fluoride-trifluoroethylene copolymer having an increased piezo-electric constant.
The present invention also relates to a polymeric piezo-electric material, capable of use as a temperature sensor, in which the polarity of the piezo-electric modulus is reversed at a specific temperature.
The present invention further relates to a polymeric piezo-electric material in which the polarity of the piezo-electric constant in the stretching direction and in a direction orthogonal to the stretching direction are opposite to each other.
2. Discussion of the Prior Art
Hitherto, polyvinylidene fluoride has been studied extensively as a polymeric piezo-electric material. A known process for preparing such a material comprises a polarization treatment including applying a high electric field at about 100.degree. C. and then cooling gradually to attain a high piezo-electric constant. However, in the case of a vinylidene fluoride-trifluoroethylene copolymer, a polymeric piezo-electric material having a high piezo-electric constant can not be obtained by the above-described process.
In prior polymeric piezo-electric materials, the polarity of the piezo-electric constant in a stretching direction has been the same as in the orthogonal direction.